BP’s latest effort to duck responsibility for the oil spill’s adverse environmental impact concerns a study of a massive die-off of bottlenose dolphins in the Gulf from 2010 through June 2013, occurring mostly after the April 2010 Deepwater Horizon blowout caused the worst oil spill in history. The study analyzes the strandings of 1,305 dolphins on the beaches or shores of the Gulf of Mexico from February 2010 through the present. About 94 percent of the stranded mammals were dead. This is the longest marine mammal die-off in the Gulf – known as an “unusual mortality event” or UME – ever recorded. In addition, the 2010 and 2011 figures for Louisiana are the highest annual numbers ever recorded for that state; for Mississippi and Alabama the 2011 figure is among the highest ever in those states.

In a carefully worded and illusory response, BP asserted that it “reiterates what other experts, such as the National Oceanic and Atmospheric Administration (NOAA), have stated: the UME started three months before the Deepwater Horizon spill, and the cause or causes have not been determined. The study does not show that the accident adversely impacted dolphin populations.”

While BP is correct in observing that the UME started in February 2010, three months before the Deepwater Horizon blowout occurred, it is more of a technical designation of the study period, rather than the identification of a starting point for an event. A look at the monthly data on dolphin strandings reveals how misleading BP’s interpretation is. Of eight data-collection sites stretching from the Texas gulf shore to Florida, the dolphin strandings in the three months before the oil spill were below average. In fact, almost all the data (minus two exceptions explained by a separate unrelated event) cited by the report show that the run of above-average strandings started in May 2010, after the spill.

It’s also true, but misleading, that the causes of the stranding and deaths “have not been determined.” The researchers acknowledge that many factors may be contributing to the dolphin die-off. But what BP doesn’t say is that the scientists have firmly determined oil as a major culprit.

The scientists observe that the most severe run of strandings occurred in Barataria Bay, La., “a coastal area heavily impacted by the spill.” They add that Barataria Bay dolphins displayed conditions, including lung disease, “consistent with adverse health effects that might be expected following oil exposure based upon the literature of documented effects in other animal species. “Outside Barataria Bay, the researchers note, “the location, timing, and magnitude of dolphin stranding trends observed following the DWH oil spill, particularly statewide for Louisiana, Mississippi, and Alabama, overlap with the location and magnitude of oil during and the year following spill.”

BP has also tried to link the dolphin die-off to brucella, an infectious bacteria. However, NOAA believes brucella is a red herring. “While brucella has been confirmed in many marine mammal species globally,” the agency says, “to date it has not been confirmed as causing epizootics [that is, unexpected increases in disease] or die-offs of multiple age classes in marine mammals, including dolphins.”